Na and Ca spikes produced by ions passing through Ca channels in mouse ovarian oocytes.

Ovarian oocyte membrane of the mouse was found to be excitable. Ca-dependent action potentials, which were blocked by Co2+, indicated the existence of Ca channels. In addition, Na-dependent action potentials were detected in Ca2+-free solution. These Na spikes were insensitive to tetrodotoxin (TTX) and were blocked by Co2+, Cd2+, or La3+, suggesting that the Na+ goes through the Ca channel instead of the Na channel. Such a Na current has not been reported in other eggs. It is concluded that both Na+ and Ca2+ pass through the Ca channels during excitation in mouse ovarian oocytes.